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Chapter 7 Firewalls. Firewall Definition. A network device that enforces network access control based upon a defined security policy. Basic Firewall Philosophy. Types of Firewalls. Circuit-level firewall verifies TCP 3-way handshake on behalf of inside hosts Proxy server firewalls
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Firewall Definition • A network device that enforces network access control based upon a defined security policy
Types of Firewalls • Circuit-level firewall • verifies TCP 3-way handshake on behalf of inside hosts • Proxy server firewalls • application aware • Proxies TCP connections on behalf of clients • not transparent to end-users • Non-stateful packet filters • Stateful packet filters • Maintains source/destination TCP/UDP port numbers, TCP sequence numbers, TCP flags, TCP session state, and UDP traffic timing based on timers • Application aware • Personal firewalls